1. Field of the Invention
The present invention relates to a photographing lens focusing apparatus, and more particularly to a focusing apparatus which is capable of speedily moving a photographing lens to a desired focus position.
2. Related Background Art
According to a method disclosed in Japanese Patent Application Laid-open No. 63-23115 filed by the applicant of the present invention, a setting position corresponding to a position of a lens at a free position is stored beforehand and the lens is made to return to the stored position.
In the above-described prior art, in addition to the requirements that there be an electrical storing apparatus for storing the position of a photographing lens and a computing apparatus for determining the difference between the position of the storing apparatus and that of the photographing lens, there is also the requirement that the difference between the position of the storing apparatus and that of the photographing lens must be monitored at all times in order to put the difference computing apparatus in an operating state. Hence, the arrangement of the circuit of the apparatus becomes complex in construction, and there is a problem in that a power cell is consumed quickly because electric current is consumed due to the above monitoring.
The construction of a lens barrel of the above-described prior art will now be explained briefly. A photographing lens is held in a helicoid and moved in a direction of the optical axis by the rotational force of a driving motor transmitted via gears. The moving of the photographing lens is controlled by signals outputted in accordance with the rotation of a slit disk disposed on an output shaft of the driving motor. Therefore, if mechanical play (backlash) occurs between the helicoid and the gears, it is inevitable that a deviation occurs in the amount of the movement of the photographing lens with respect to the above signals.